In the last decade embryo transfer technology has been the focal point of research in the industry of farm animal production because it allows one to obtain progeny from a female with superior productive characteristics relative to the average of the breed. This results in offspring, in recipients cows, far superior to that which could be obtained from those cows under natural conditions.
The history of embryo transfer goes back to the 17th century. In 1672, Mr. Fegnier de Graff first saw and recognized the fertilized rabbit ovum in the blastocyst stage. It was not until the 19th century, however, that an offspring as a result of embryo transfer was first obtained by Mr. Walter Heape working with rabbits. In 1951 the first calf produced from a surgical transfer was reported by Mr. Willet at the University of Wisconsin.
People soon saw the commercial and productive advantages that this technique could offer. Thus, simpler methods were created and developed. In the late 1970's, the first collection and embryo transfer took place without surgery and the technology began to be applied directly by cattlemen on farms or ranches. The non-surgical methods utilized a transvaginal approach to the uterus via a series of hoses through which the medium of collection was injected until the uterus was distended. Normally, the medium was discharged through another hose into a graduated vessel, big enough to hold 1.5 liters of the medium. It was very inconvenient to search for and find, the embryos in all that medium under the microscope.
These inconveniences led to the development of filter devices. Through the use of a net filter in a small vessel it was possible to collect the embryos while letting more than 90% of the liquid pass. This collection device was introduced during the middle 1980's. It was not until later that a new device, with innovative characteristics of automatic control in the filtering and draining of the collected medium was introduced. This new device has its own system of ventilation with a device for the localization, manipulation and evaluation of the embryo. As explained below, however, these devices present great disadvantages as compared to the present invention.
The most common filter now used is a small container with a filter net and drain in the bottom of the device. The drain has an entrance that has an internal diameter smaller that the hoses of collection. This causes an increase or build up of momentary pressure that results in strong turbulence as the medium drains. This leads to formation of a foam, and the embryos adhering or sticking more tightly to the uterine mucus. This makes the job difficult for the observer trying to locate the embryos. It is also necessary in most of the cases, to wait until the foam dissolves before locating and evaluating the embryos. Another great disadvantage of this filter is, that the embryos get easily entrapped between the uterine mucus and the filtration net located at the bottom. Although this filter has a larger filtration net than that of the present invention, it has the inconvenience that the drainage tube is of a smaller diameter, which produces a strong suction that causes embryos and uterine mucus to gather at the net.
In some uterus flushes with a lot of mucus, the filtering and the draining is very slow and as a consequence this retards considerably the task of collection, and in extreme cases necessitates use of another filter. It also creates the need to control flow with a clamp that is placed on the hose connected to the draining tube. The inconvenience of this procedure is that it requires a technician or an assistant to control the outflow making sure that: the filter will not fill up completely, or exploding and overflow; and that the filter will not run dry, thus removing the embryos from the medium and exposing them to a potentially hostile environment.
Another inconvenience of this filter is that the localization, manipulation and embryonic evaluation cannot be solely done within the device, therefore what is required are other steps and devices in the process of collection and evaluation once the uterine wash has been completed. Specifically, the filter is drained until all that remains is approximately 1/5 of its volume. It is then shaken forming a whirl that it able to remove most of the embryos from the filter device. The medium is then poured into a petri dish, the filtration net must be washed immediately with a syringe full of the collection medium utilizing a needle of a small caliber (less than 18 gauge). This is in order to loosen as much of the uterine mucus and entrapped embryos as possible. With this method there is a risk of causing physical damage to the embryo by the trauma they suffer while being agitated and poured into the petri dish and also being hit by the stream of medium under pressure. This risk is eliminated by using the device of the present invention.
Furthermore, the localization and evaluation of the embryo in the conventional petri dish is more tedious than with the improved device of the present invention. In addition to having a large surface area for searching, the petri dish has vertical walls, which make it difficult to find embryos stuck to them, because the walls reduce the visibility in the perimeter of the petri dish, this is not the case with the improved device of the present invention.
There are other designs of filters on the market that differ only in their capacity of volume. These filters are self-draining because they have in the center a plastic tower that rises from its base to continue to the top of the device in a net of filtration. But such filters act the same as the filter with its filtration net at the bottom, receiving in cascade the collected medium. The mucus and the embryos easily slide towards the filtration net. Once the collected medium has all passed, it is necessary to let the medium settle for several seconds, then the remaining liquid in the filter is sucked up with a syringe down below the inferior level of the net. The removal of the liquid is necessary to prevent (continued leakage from) the filter choice as it is moved and the glass base of the microscope getting wet with interruption of visibility. This is another of the differences that exist in the collection and evaluation of embryos using the improved device.